av_find_input_format(const char *short_name)；方法分析.使用 av_find_input_format 打开摄像头，麦克风

函数原型 和 源码实现

/**
 * Find AVInputFormat based on the short name of the input format.
 */
ff_const59 AVInputFormat *av_find_input_format(const char *short_name);

根据 AVInputFormat 的短名字 来找到具体的 AVInputFormat。从源码实现可以看到：最终是从 demuxer_list 数组中找，找完 demuxer_list 数组，再从 indev_list数组中找

ff_const59 AVInputFormat *av_find_input_format(const char *short_name)
{
    const AVInputFormat *fmt = NULL;
    void *i = 0;
    while ((fmt = av_demuxer_iterate(&i)))
        if (av_match_name(short_name, fmt->name))
            return (AVInputFormat*)fmt;
    return NULL;
}

const AVInputFormat *av_demuxer_iterate(void **opaque)
{
    static const uintptr_t size = sizeof(demuxer_list)/sizeof(demuxer_list[0]) - 1;
    uintptr_t i = (uintptr_t)*opaque;
    const AVInputFormat *f = NULL;

    if (i < size) {
        f = demuxer_list[i];
    } else if (outdev_list) {
        f = indev_list[i - size];
    }

    if (f)
        *opaque = (void*)(i + 1);
    return f;
}

 先从demuxer_list数组中找

static const AVInputFormat * const demuxer_list[] = {
    &ff_aa_demuxer,
    &ff_aac_demuxer,
    &ff_aax_demuxer,
    &ff_ac3_demuxer,
    &ff_ace_demuxer,
    &ff_acm_demuxer,
    &ff_act_demuxer,
    &ff_adf_demuxer,
    &ff_adp_demuxer,
    &ff_ads_demuxer,
    &ff_adx_demuxer,
    &ff_aea_demuxer,
    &ff_afc_demuxer,
    &ff_aiff_demuxer,
    &ff_aix_demuxer,
    &ff_alp_demuxer,
    &ff_amr_demuxer,
    &ff_amrnb_demuxer,
    &ff_amrwb_demuxer,
    &ff_anm_demuxer,
    &ff_apac_demuxer,
    &ff_apc_demuxer,
    &ff_ape_demuxer,
    &ff_apm_demuxer,
    &ff_apng_demuxer,
    &ff_aptx_demuxer,
    &ff_aptx_hd_demuxer,
    &ff_aqtitle_demuxer,
    &ff_argo_asf_demuxer,
    &ff_argo_brp_demuxer,
    &ff_argo_cvg_demuxer,
    &ff_asf_demuxer,
    &ff_asf_o_demuxer,
    &ff_ass_demuxer,
    &ff_ast_demuxer,
    &ff_au_demuxer,
    &ff_av1_demuxer,
    &ff_avi_demuxer,
    &ff_avr_demuxer,
    &ff_avs_demuxer,
    &ff_avs2_demuxer,
    &ff_avs3_demuxer,
    &ff_bethsoftvid_demuxer,
    &ff_bfi_demuxer,
    &ff_bintext_demuxer,
    &ff_bink_demuxer,
    &ff_binka_demuxer,
    &ff_bit_demuxer,
    &ff_bitpacked_demuxer,
    &ff_bmv_demuxer,
    &ff_bfstm_demuxer,
    &ff_brstm_demuxer,
    &ff_boa_demuxer,
    &ff_bonk_demuxer,
    &ff_c93_demuxer,
    &ff_caf_demuxer,
    &ff_cavsvideo_demuxer,
    &ff_cdg_demuxer,
    &ff_cdxl_demuxer,
    &ff_cine_demuxer,
    &ff_codec2_demuxer,
    &ff_codec2raw_demuxer,
    &ff_concat_demuxer,
    &ff_data_demuxer,
    &ff_daud_demuxer,
    &ff_dcstr_demuxer,
    &ff_derf_demuxer,
    &ff_dfa_demuxer,
    &ff_dfpwm_demuxer,
    &ff_dhav_demuxer,
    &ff_dirac_demuxer,
    &ff_dnxhd_demuxer,
    &ff_dsf_demuxer,
    &ff_dsicin_demuxer,
    &ff_dss_demuxer,
    &ff_dts_demuxer,
    &ff_dtshd_demuxer,
    &ff_dv_demuxer,
    &ff_dvbsub_demuxer,
    &ff_dvbtxt_demuxer,
    &ff_dxa_demuxer,
    &ff_ea_demuxer,
    &ff_ea_cdata_demuxer,
    &ff_eac3_demuxer,
    &ff_epaf_demuxer,
    &ff_ffmetadata_demuxer,
    &ff_filmstrip_demuxer,
    &ff_fits_demuxer,
    &ff_flac_demuxer,
    &ff_flic_demuxer,
    &ff_flv_demuxer,
    &ff_live_flv_demuxer,
    &ff_fourxm_demuxer,
    &ff_frm_demuxer,
    &ff_fsb_demuxer,
    &ff_fwse_demuxer,
    &ff_g722_demuxer,
    &ff_g723_1_demuxer,
    &ff_g726_demuxer,
    &ff_g726le_demuxer,
    &ff_g729_demuxer,
    &ff_gdv_demuxer,
    &ff_genh_demuxer,
    &ff_gif_demuxer,
    &ff_gsm_demuxer,
    &ff_gxf_demuxer,
    &ff_h261_demuxer,
    &ff_h263_demuxer,
    &ff_h264_demuxer,
    &ff_hca_demuxer,
    &ff_hcom_demuxer,
    &ff_hevc_demuxer,
    &ff_hls_demuxer,
    &ff_hnm_demuxer,
    &ff_ico_demuxer,
    &ff_idcin_demuxer,
    &ff_idf_demuxer,
    &ff_iff_demuxer,
    &ff_ifv_demuxer,
    &ff_ilbc_demuxer,
    &ff_image2_demuxer,
    &ff_image2pipe_demuxer,
    &ff_image2_alias_pix_demuxer,
    &ff_image2_brender_pix_demuxer,
    &ff_ingenient_demuxer,
    &ff_ipmovie_demuxer,
    &ff_ipu_demuxer,
    &ff_ircam_demuxer,
    &ff_iss_demuxer,
    &ff_iv8_demuxer,
    &ff_ivf_demuxer,
    &ff_ivr_demuxer,
    &ff_jacosub_demuxer,
    &ff_jv_demuxer,
    &ff_kux_demuxer,
    &ff_kvag_demuxer,
    &ff_laf_demuxer,
    &ff_lmlm4_demuxer,
    &ff_loas_demuxer,
    &ff_luodat_demuxer,
    &ff_lrc_demuxer,
    &ff_lvf_demuxer,
    &ff_lxf_demuxer,
    &ff_m4v_demuxer,
    &ff_mca_de